Motion transforming device with screw-and-nut transmission is described for instance in a German Patent DE 3121136. State of the art of motors in a tube and screw-and-nut transmissions is represented by following patents: GB 857,203, DE1 957658, U.S. Pat. No. 2,818,743 a U.S. Pat. No. 4,723,453. Existing motors in a tube use screw transmission where both guide and driving nuts are manufactured by milling of both axial and helical groove on tube and both guide and driving nuts are coaxial.
Disadvantage of such an arrangement is in that it cannot work at high specific torques, related to the cross-section of the transmission. Otherwise, there are motors in a tube used with planetary gearbox, however, they have the same disadvantage.